Process for the manufacture of dibenzanthronyls



Patented Bee. 31, 1946 UNITED STATES PA'rsNr orrlce PROCESS FOR THEMANUFACTURE OF DIBENZANTHRONYLS Henry R. Lee, Pitrnan, N. J., and EdwardT. Howell, Wilmington, Del, assignors to E. I. du'Pont de Nemours &Company, Wilmington, Del a corporation of Delaware No Drawing..Application March 27, 1946, Serial No. 657,612

This invention relates to an improvement in the process of themanufacture of dibenz'anthronyls, andtmore particularly, to an improvedprocess for carryingout the c'ondensationof benzanthrone and its simplesubstitution derivatives to Bz-1:Bz- Y-dibenzanthronyls'.

In the Conversion of benzanthrone to 32-1132- l-dibenZanthronyl, thecondensation has heretofore been carried out i'riconcentrated sulfuricacid by means" of an oxidizing agent such as manganese dioxide, chromicacid, etc. The conversion, as originally described in German Patent431,774; was exceptionally low,' and a high per centage of oxidationproducts were produced, It was later found that; if the condensation wascarried out under more mild conditions and stopped at a point where from36% to 40% of benzanthrone remaine' d' unchanged in the reaction mass, ahigher totalconversion to 332-1 :32- l"-diben'zant'hronyl could beobtained. This-prom ess, however, requires the recovery of thebenzanthrone if comparatively high yields of theBz-i:Bz-1-dibenzanthronyl are to beobtained based on the totalbenz'anthrone' employed;

Irrespective of how the oxidation of the benzant-hrone has heretoforebeen carried out, side react-ions inevitably takeplace which produceoxo-derivative's of bothbenzanthrone and dibenzant-hrcnyl, and theseremain as impurities in the final product. On reduction of theseoxoderivatives, such as with sulfurous acid, they are in the mainconverted to h-ydroxy compounds which will be referred tohereaftergenerally as oxy bodies. A description of these o-xy bodies maybe found in Examples 1 and 4 of British Patent 251,313. While some ofthe oXy bodies are soluble in aqueous alkaline solutions, others,although apparently forming alkali metal salts, are not sufli'cientlysoluble to be removed by an alkali'ne extraction, and it has'been foundthat certain of the oxy derivatives'of Bz-1:B'z--1'-dibenz anthronylwere-notremoved by previous methods of separation and were thereforepresent with the Bz-lzBz-l -dibenzanthronyl as a mixture which hasheretofore been mistaken for the 32-1 :Bz-l -dibenzanthronyl itself.

It is an object of the present invention to provide an improved processfor the preparation of 182-1 :Bz-1'-dibenzanthronyl and its simplemonovalent substitution derivatives, whereby higher yields of theBz-l:Bz-l-dibenzanthrony1 are obtained and the amoLmt of oxy-bodies asimpurities is materially reduced.

We have now found that, where alkyl sulfuric acids are used in place ofsulfuric acid as the sol- 2 Claims. (01. 260'36 3) vapor reactionmedium, much higher yields of the Bz-l:Bz-l -dibenzanthronyl of a higherpurity are obtained than has heretofore been possible without reworkingthe unchanged benzanthrone, which offers difficulties on a commercialscale, The, alkyl sulfuric acids are preferably the methyl sulfuric acidand ethyl sulfuric acid. When using these alkyl sulfuric acids, aslittle as from 5 to '7 parts of the alkyl sulfuric acid may beemployedper part of benzanthrone to be oxidized. Larger proportions maybe employed, al-

though the use of unnecessarily large amounts will, of course, make theprocess less economical.

The oxidizing agents employed are those which have previously been usedwith sulfuric acid, such as manganese dioxide and chromic acidanhydride. used Will be varied, depending upon the amount of solventemployed, although usually it will be found that from 3 to 5 mols ofmanganese dioxide (106% pure basis) per mol' of benzanthrone will give asatisfactory conversion of the benzanthrone to the dibenzanthronyl Theoxidation is preferably carried out at temperatures of from 5 to 20 C.,although lower or higher temperatures may be employed.

The alkyl sulfuric acid is preferably made as a preliminary step incarrying out the oxidation of the benzanthrone. In the preparation ofthe alkyl sulfuric acid by the addition of anhydrous alcohols tochlorosulfonic acid at low temperatures, there is usually present in theresulting alkyl sulfuric acid a small amount of sulfuric acid, but ithas been found that the presence of this small amount of sulfuric acidis not detrimental in carrying out the oxidation of the benz anthrone,While there is also present in the alkyl sulfuric acid some residualhydrochloric acid, this can be largely eliminated by air-blowing or byblowing an inert gas through the alkyl sulfuric acid when formed. It hasbeen found, however, that the presence of small amounts of hydrochloricacid up to 0.75% does not materially affeet the resulting oxidationreaction.

The presence of excess alcohol or water in the alkyl sulfuric acid,however, retards the subsequent oxidation of the benzanthrone and givesan unnecessarily high amount of unchanged benzanthrone in the finalproduct. For best results, the alkyl sulfuric acid should be anhydrousand free from alcohol.

For purposes of this invention, We do not wish to be limited to anyparticular method of formation of the alkyl sulfuric acids.

lhe amount of oxidizing agent to be 3 The following example is given toillustrate the invention. The parts used are by weight.

Example 1078 parts of chlorosulfonic acid are charged into a closedenamel lined kettle fitted with agitator and cooling jacket. The chargeis cooled to l C. and 302 parts of anhydrous methanol are slowly run inwith cooling at such a rate that the temperature does not exceed 0 C.Hydrochloric acid, which is copiously evolved, is vented ofi. After allof the methano1 has been added, the temperature of the mass is raised tofrom 20 to'25 C. and dry air or an inert gas is blown through until onlytraces of hydrochloric acid come out of the vent.

1000 parts of the above methyl sulfuric acid are charged into a closediron or steel kettle fitted with agitator and cooling bath. 200 parts ofpurified benzanthrone are charged in and the solution is cooled to from'-5 to 0 C. 370 parts of 81.6% manganese dioxide are added with coolingat such a rate that the temperature does not exceed C. After all of themanganese dioxide has been added, the reaction mass is stirred at from-5 to 0 C. until no further reaction takes place. This may require about20 hours. The reaction mass is discharged into 5000 parts of watercontaining 370 parts of sodium bisulfite. 400 parts of concentratedsulfuric acid are added and the slurry is heated to the boil. Moresodium bisulfite is added if an excess of sulfur dioxide is notdetected. 5000 parts of cold water are added and the suspension isfiltered off and washed acid-free. If not completely free from manganesedioxide, the filter cake is milled and given an additional bisulfitetreatment with sulfuric acid, and is then filtered, washed acid-free anddried. Calculated to the ash-free basis, the average analysis shows a70.0% yield of Bz-l :Bz- 1'-dibenzanthronyl.

A yield of 70% by this process is compared with a direct yield of from40% to 55% of B2- 1:Bz-1'-dibenzanthronyl when the condensation iscarried out according to the processes of Examples 2 or 3 of U. S.Patent 2,001,063, when the yields are calculated on the basis of an acidrecrystallization and purification carried out as follows:

Ten parts of the crude Bz-1:Bz-1'-dibenzanthronyl, as obtained directlyby the condensation as described above, are dissolved in 100 parts of95% sulfuric acid at from 25 to 30 C. 28 parts of water are added atsuch a rate that the temperature rises gradually to 100 C., and the rateis then adjusted so that the rest of the water is added at from 90 to100 C. The mass is allowed to cool to from 25 to 30 C. with agitation.The microscope shows rod-like crystals of a size suficient to filterrapidly. The crystals are filtered on a porous plate filter and arewashed with 100 parts of 75% sulfuric acid. The crystals are digested inwater, filtered, washed with water and digested in dilute caustic sodasolution. The slurry is filtered, washed alkalifree and dried. Theweight of this dried product, when compared with the original amount oflbenzanthrone employed in the condensation, is used as the yield ofBz-1:Bz-1'-dibenzanthronyl obtained by the process involved.

When ethyl sulfuric acid is substituted for the methyl sulfuric acid inthe above example, a similar improvement in yields of a relatively pureBz-lzBz 1'-dibenzanthronyl is obtained. The ethyl sulfuric acid employedmay be produced as follows:

621 parts of chlorosulfonic acid are charged into a closed enamel linedkettle fitted with agitator and cooling jacket. The charge is cooled to-10 C. and 245 parts of absolute ethyl alcohol are slowly run in withagitation and cooling so that the temperature does not exceed 0 C. Thehydrochloric acid gas evolved is vented off. When all of the alcohol hasbeen added, the mass is allowed to warm to from 20 to 25 C. and is blownwith dry air until practically free from hydrochloric acid.

6 methyl benzonthrone, 6 chloro benzanthrone, or other halogen or methylderivatives of benzanthrone which do not contain the halogen or methylin the 2- or Bz-l-positions, can be converted to the correspondingBz-1:Bz-1-dibenzanthronyl in the manner illustrated in the aboveexample. Similar improvements in yield and purity of the resultingdibenzanthronyl are obtained.

The use of methyl or ethyl sulfuric acid not only increases the yield ofthe desired Bz-lzBz- 1'-dibenzanthronyl but permits a material increasein the production of the dibenzanthronyl per unit of equipment, for,while with the methyl andethyl sulfuric acid only from 5 to 7 parts arerequired per part of benzanthrone, when using sulfuric acid as thesolvent, optimum yields of the dibenzanthronyl are obtained only when atleast 15 parts of sulfuric acid are employed per part of benzanthrone.

We claim:

1. In the process for preparing Bz-l:Bz-1'-dibenzanthronyl and itshalogen and methyl derivatives wherein condensation of the benzanthronecompound is effected by means of an oxidizing agent, the step whichcomprises carrying out the condensation of the benzanthrone compound inan alkyl sulfuric acid of the class consisting of methyl sulfuric acidand ethyl sulfuric acid, the reaction being carried out at temp-eraturesof from -5 to 20 C. p

2. In the process for preparing Bz-1:Bz-1-dibenzanthronyl and itshalogen and methyl derivatives wherein condensation of the benzanthronecompound is effected by means of an oxidizing agent, the step whichcomprises carrying out the condensation of the benzanthrone compoundwith manganese dioxide in an alkyl sulfuric acid of the class consistingof methyl sulfuric acid and ethyl sulfuric acid, the reaction beingcarried out at temperatures of from -5 to 20 C.

HENRY R. LEE. EDWARD T. HOWELL.

